Internet giants including AOL have promised to take legal action against spam merchants who clog up email users' mailboxes with porn, get rich quick schemes and advertising once a new European directive against the practice comes into force later this week.

MPs and internet users have warned the spam epidemic is threatening to bring email to a standstill, with recent surveys estimating that by February seven out of every 10 emails will be unwanted spam, compared with 8% two years ago.

The new EU privacy and communications directive comes into force tomorrow and will ban marketing companies from bombarding potential customers with unwanted mail unless they already have agreed or have a "prior business relationship" with the company.

Retailers have increasingly turned to email marketing over the past two years as a new way to reach potential customers.

They have 12 weeks to adapt to the new regulations before facing the possibility of a £5,000 fine, rising to an unlimited fine that could run into hundreds of thousands of pounds if they are successfully prosecuted.

The new rules were finally agreed earlier this year following months of wrangling between EU member states over whether customers should have to "opt in" to receive emails or "opt out" of receiving them.

In the end, the EU passed a limited version of "opt in" allowing for some latitude if a customer had previously handed over their details.

AOL has pledged to use the new directive to take legal action against persistent spammers where possible - but has also warned the new rules may not be strict enough to deter the persistent spammers that have become the bane of many email users' lives.

"The UK government will certainly need to coordinate with other countries to ensure cross border consistency. We may also need stronger penalties than are currently in place against those who transgress the new guidelines if they are to be fully effective," said a spokesman.

Internet service providers have begun to put more resources into spam blocking software with the likes of BT Yahoo!, AOL and Freeserve promoting it as a key feature of their connection offerings.

But several companies who supply software to block spam have said the new rules are unlikely to provide much protection against the kind of mass email campaigns sent from the US and other countries that clog up inboxes on a daily basis.

"This move signifies a growing lack of tolerance to the problem with the authorities, and in that respect it's encouraging," said Alyn Hockey, the director of research at technology company Clearswift.

"But what about all the mail emanating from abroad? It's hardly going to discourage the spamming hardcore from peddling their wares," he added.

Others fear the new regulations could be rendered useless if the US Congress does not pass similar rules. America continues to follow a policy that requires computer users to opt out of receiving spam.

"Unless the US plays ball, I think servers around the world will start to pack up by February," said Labour MP Derek Wyatt, speaking earlier this year before leading a delegation of MPs to Washington to campaign for a change in the law.